Practice Quiz

Civil Engineering PE

Category - Transportation

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Approximately how long will it take for a truck to go from 55 mph to a complete stop if it is decelerating at a rate of 5 feet/second/second?
  1. 11 seconds
  2. 16 seconds
  3. 62 seconds
  4. None of the above
Explanation
Answer: B - It will take approximately 16 seconds for a truck that goes from a 55 mph to a complete stop when decelerating at a rate of 5 feet/second/second.

Solution: Use the final velocity formula to solve for time

vf = vo + at

Where

vf = 55 mph

vo = 0 mph

a = -5 feet/second/second

Therefore,

55 mph = 0 mph + 5 feet/second/second* (t)

t = [55 mph *(1 hour/3,600 seconds) (5,280 feet/mile)]/5 feet/second/second

t = 16 seconds
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